Infrared sensitization of photoconductive compositions employing cyanine dyes

ABSTRACT

Photoconductive compositions comprising zinc oxide are sensitized in the near infrared region of the spectrum by near infrared-sensitizing cyanine dyes. The dyes adsorb onto the surface of zinc oxide and render it photosensitive to wavelengths of light above 700 millimicrons.

[72] inventors United States Patent Glnncarlo A. Cavagna Adelphi;

Asa Leiler, Beltsville; Fredric N. Miller, Laurel; Frederick J.Vermllllon, Jr., Wheaton, all of Md.

July 30, 1968 Nov. 9, 197 l Westvaeo Corporation New York, N .Y.

[21 Appl. No. [22] Filed [45] Patented [73] Assignee 52 u.s. c1 96/l.7R, 96/130 R, 260/2405 R 511 1m.c1 G03g 5/00, 003C 1/08 [50] FieldolSearch 96/l.5, L7, 1.8; 260/2405 [56] References Cited UNITED STATESPATENTS 3,l 2 l .006 2/1964 Middleton et al 96/l 3,080,363 3/l963Horwitz et al. 260/2406 3,245,786 4/1966 Cassiers et al.. 96/] PrimaryExaminer-Charles E Van Horn Assismnl ExaminerM. WittenbergAttorneys-Richard Lv Schmalz and Robert S. Grimshaw ABSTRACT:Photoconductive compositions comprising zinc oxide are sensitized in thenear infrared region ofthe spectrum by near infrared-sensitizing cyaninedyes. The dyes adsorb onto the surface of zinc oxide and render itphotosensitive t0 wavelengths of light above 700 millimicrons.

PATENTEDNUV 9 I971 3.6 l 9 1 54 l/(vo/Is) f (Seconds) FIG. 2

Wvo/fs) o 1 l 1 l l l l .f (Seconds) v (wits) Brornophenol Blue l l l l1 J 4 6 3 INVENTORS I (Seconds) ammo/191.0 A. cAvAan/A ASA LE/FER mean/01v. MILLER FREDERICK .1. VERM/LL/OMJR M M ATTORNEY INFRAREDSENSITIZATION OF PHOTOCONDUCTIVE COMPOSITIONS EMPLOYING CYANINE DYESBRIEF SUMMARY OF THE INVENTION This invention relates to photoconductivecompositions and more particularly to photoconductive compositionscomprising zinc oxide having absorbed on the surface thereof a nearinfrared-sensitizing cyanine dye.

It is known that zinc oxide can be employed in making photoconductivelayers on ordinary paper and that photographic copies can be preparedfrom these photoconductive papers. In one process, the zinc oxide layeris exposed to a photographic image, and a latent image is formed on thezinc oxide which can be developed into a photographic copy. In anotherprocess, the developed image is transferred from the zinc oxide sheet toa receiving sheet to make a photographic copy.

Zinc oxide normally has a spectral response in the ultraviolet region ofthe spectrum, at about 386 millimicrons. For an electrophotographicprocess, zinc oxide is generally sensitized to be responsive in thevisible region of the spectrum at a wavelength between about 500 to 620millimicrons, by the addition of low concentrations of dyes. Cyaninedyes are known in this connection as shown in U.S. Pat. No. 3,128,179.However, while the dyes there disclosed are satisfactory forsensitization of zinc oxide in the visible region, they do not providesensitization above 700 millimicrons, the infrared region of thespectrum.

As is known, photoconductive layers comprising zinc oxide are generallyplaced on a paper support which when grounded is given a negativeelectrostatic charge on the zinc oxide layer, usually by means of iontransfer from a corona discharge. When the photoconductive layer isexposed to a photographic image, the unexposed portions of the zincoxide layer retain their negative electrostatic charge while the exposedportions of the photoconductive layer, which receive visible orultraviolet radiation, lose some or all of their negative electrostaticcharge. The resulting latent image represented by the unexposed portionsof the photoconductive layer can be developed by use of a toner powderwhich has an electrostatic charge opposite to the negatively chargedunexposed portions of the photoconductive layer. The toner powder isthus at tracted to the unexposed portions and is affixed thereto bymelting the resin contained in the toner powder so that the tonerparticles fuse to the surface of the photoconductive layer to provide apermanent copy.

In the past, the zinc oxide layer has been exposed in a copy machine,such as the SCM Electrostatic Copier, which uses a tungsten lamp for theexposure. We have found that while the conventional zinc oxide sheet issensitized with dyes to be responsive in the visible region of thespectrum, about 80 percent of the light emitted from a tungsten lamp isin the near infrared, the spectral region above about 700 millimicrons.It can be seen, therefore, that the electrophotographic process can bemade more efficient by sensitizing zinc oxide in the near infraredregion of the spectrum. Further, we have found that the intensity of theexposing source can be greatly reduced and excellent prints obtainedwhen zinc oxide is sensitized in the near infrared region of thespectrum. Under the same conditions of low intensity, a standard zincoxide photoconductive layer, sensitized in the known manner in thevisible region of the spectrum, will not yield a print.

By use of near infrared-sensitizing dyes for zinc oxide, another problemwith present zinc oxide papers can be overcome. Even though thepresently known dyes for sensitizing zinc oxide in the visible region ofthe spectrum are used in low concentrations, the dyes in many instancesimpart an undesirable color to the zinc oxide coated papers. Forexample, uranine and Rose Bengal impart a pink color to the zinc oxideelectrophotographic layer, and bromophenol blue tends to impart a purplecolor. With the use of an infrared-sensitizing dye, theelectrophotographic layer absorbs little, if any, light in the visibleregion of the spectrum. The result is that the infraredsensitizing dyedoes not tend to color the zinc oxide layer, and the final productappears whiter and has a higher luminosity.

The types of dyes which can be used in practicing our invention comprisethose dyes which can sensitize zinc oxide in the near infrared region ofthe spectrum, i.e., between 700 and 2,000 millimicrons. In particular,we have found that cyanine or polymethine dyes having at least a sevencarbon chain (heptamethine structure) bridging two heterocyclic nucleiare quite useful in practicing the present invention. In general, thesedyes can be represented by the following general formula:

wherein R and R each represents a member selected from the groupconsisting of an alkyl group (e.g., methyl, ethyl, propyl, etc.), ahydroxyalkyl group (e.g., hydroxyethyl, hydroxypropyl, etc.), analkoxyalkyl group (e.g., B-methoxyethyl, B- ethoxyethyl, etc.), acarboxyalkyl group (e.g., carboxymethyl, fi-carboxyethyl, etc.), acarbalkoxyalkyl group (e.g., carbomethoxymethyl, B-carbomethoxyethyl,etc.), an acyloxyalkyl group (e.g., B-acetoxyethyl, 'y-acetoxypropyl,etc.), and an aralkyl group (e.g., benzyl, fi-phenethyl, etc.); Rrepresents a hydrogen atom, an alkyl group, an aryl group (e.g., phenyl,hydroxyphenyl, etc. or an acetoxy group; q represents a positive integerfrom 1 to 3; X represents an acid anion (e.g., chloride, iodide,methylsulfate, ethylsulfate, p-toluenesulfonate, etc.); and Z and Z eachrepresents the nonmetallic atoms necessary to complete a heterocyclicnucleus selected from the group consisting of a thiazole nucleus (e.g.,thiazole, methylthiazole, phenylthiazole, etc.), a benzothiazole nucleus(e.g., benzothiazole, -chlorobenzothiazole, 6-methylbenzothiazole,etc.), a naphthothiazole nucleus e.g., a or B- naphthothiazole,S-ethoxy-Bnaphthothiazole, etc.), an oxazole nucleus (e. g.,4-methyl0xazole, 4-phenyloxazole, etc. a benzoxazole nucleus (e.g.,benzoxazole, o-chlorobenzoxazole, etc.), a naphthoxazole nucleus e.g., aor B-naphthoxazole, 5- methoxy-B-naphthoxazole, etc.), a selenazolenucleus (e.g., selanazole, 4-methyselenazole, 4-phenylselenazole, etc.),a benzoselanazole nucleus (e.g., benzoselenazole, 5-chlorobenzoselenazole, etc.), a naphthoselenazole nucleus (e.g., a orfl-naphthoselenazole, 5-ethoxy-B- naphthoselenazole, etc.), aZ-quinoline nucleus (e.g., quinoline, S-methylquinoline,6-chloroquinoline, etc.), a 4-quinoline nucleus (e.g., quinoline,6-methoxyquinoline, etc.), a lisoquinoline nucleus (e.g., isoquinoline,3,4-dihydroisoquinoline, etc.), and a 3,3-dialkylindolenine nucleus(e.g., 3,3- dimethylindolenine, 3,3,5-trimethylindolenine, etc.),provided that at least one of the groups R, R R Z, or Z contains a sulfogroup (e.g., sulfo, sulfoalkyl such as m-sulfoethyl, m-sulfopropyl,etc.) or a carboxy group (e.g., carboxy, w-carboxyethyl,w-carboxypropyl, etc.

Those skilled in the art of dye sensitization will readily appreciatethat the anhydronium bases of the above dyes will be equally effectiveas near infrared-sensitizing dyes for zinc oxide. The anhydronium basesare regarded as being derived from the above general formula by the lossof a mole of l-IX or MX wherein X has been defined above and M is ametallic atom such as sodium, potassium, etc. The anhydronium bases ofthe above dyes are within the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWING FIGS. 1 and 2 represent the curvesobtained when electrophotographic layers containing infrared-sensitizingdyes were tested for electrophotographic speed in a dynamic capacitanceelectrometer.

FIG. 3 represents the curve obtained when an electrophotographic layercontaining a conventional sensitizing dye was tested forelectrophotographic speed in a dynamic capacitance electrometer.

DETAILED DESCRIPTION SYNTHESIS OF [Z-BIS (3- m-CARBOXYETHYLBENZOTHIAZOLYL HEPTAMETHINE CYANINE IODIDE (IR-1) To 600 ml. of absoluteethanol were added 70 g. of 2- methyl-3-(w-carboxyethyl) benzothiazoleiodide (0. 2 mole) and 30 g. of glutaconic dianil hydrochloride (0.1 1mole), and the mixture thereof was heated to its boiling point, about 85C. The'heating was then discontinued and 30 g. of sodium ethylate in 150ml. of absolute alcohol were slowly added over a period of time of about5 minutes. The reaction was allowed to continue for an additionalminutes, and the product was allowed to cool to and was kept at roomtemperature for about 36 hours. The product was then placed in arefrigerator set at about -l0 C. for about 24 hours, and blue-black dyeprecipitated. The dye was filtered, suspended in ether three times, thenin ethanol, and finally in ether. The yield of dye was about 100 g. Thedye melted over a temperature range of about 21 8 to 230 C. Theprincipal absorption maximum, as measured on a DK-ZA AbsorptionSpectrophotometer, for the dye appeared at 760 millimicrons in dilutedimethyl sulfoxide. When absorbed on zinc oxide, the absorption maximum,as measured on a DK-2A Reflectance Spectrophotometer, was about 780millimicrons. An analysis of the infrared spectrum of the dye, obtainedwith a Perkin-Elmer 521 Grating Infrared Spectrophotometer, indicatedHthat most of the dye was present as the sodium salt of the carboxyl- 1cacid. However, the dye has also been prepared in the form of the freecarboxylic acid in which form it is equally as effective as aninfrared-sensitizer for zinc oxide.

SYNTHESIS OF [Z-BlS (3 w-SULFOPROPYL To 50 ml. of dry ethanol were added5.42 g. of 2-methyl-3- (w-sulfopropyl) benzothiazole (0.02 mole) and2.84 g. of glutaconic dianil hydrochloride (0.0] mole), and the mixturewas brought to a boil. The heating was then discontinued and 1.5 g. ofsodium ethylate in 30 ml. of dry ethanol were slowly added over a periodof time of about 5 minutes. The mixture was heated at about C. for about5 minutes, then allowed to cool to and remain at room temperature in thedark for about 60 hours. The mixture was then refrigerated at about 10C. for about 24 hours. The crude dye which precipitated was filtered,washed with 200 ml. of ethanol, and dried with ether. The yield wasabout 7.5 g. The dye melted at about l98200 C. The principal absorptionmaximum for the dye appeared at 770 millimicrons in dilute ethanol. Whenabsorbed on zinc oxide, the absorption maximum was about 800millimicrons. An analysis of the infrared spectrum of the dye indicatedthat the cyanine dye was obtained in the form of sodium salt of thesulfonic acid. However, the dye has also been prepared in the form ofthe free sulfonic acid and has been found to be equally as effective asan infrared-sensitizing dye for zinc oxide.

Dyes lR-l and lR-2 are the preferred dyes for the purposes of thepresent invention. However, as will be readily appreciated in view ofthis disclosure, other polymethine dyes having the general structuredescribed previously can be used to sensitize zinc oxide in the nearinfrared region of the spectrum.

SYNTHESIS OF [Z-BIS (3 w-sulfopropyl B- NAPl-ITl-IOTHIAZOLYLHHEPTAMETHINE CYANINE To 30 ml. of dry ethanol were added 3.25 g. of2-methyl-3- (w-sulfopropyl) ,B-naphthothiazole (0.01 mole) and 1.45 g.of glutaconic dianil hydrochloride (0.005 mole), and the mixture washeated to approximately 85 C. The heating was then discontinued and 0.5g. of sodium ethylate in 10 ml. of dry ethanol were slowly added, withstirring, over a period of time of about 5 minutes. The reaction mixtureturned red, then slowly turned to dark green. lt was kept in the dark atroom temperature for about l6 hours and then refrigerated at about -l0C. for about 20 hours. The crude dye which precipitated 0 was filtered,washed with 200 ml. of cold ethanol, then was suspended in warm ethanol,filtered, and rinsed first with cold ethanol and finally with ether Theyield was about 3.l g. The dye melted over a temperature range of about218 to 235 C. The principal absorption maximum for the dye appeared at803 millimicrons in methanol. When adsorbed on zinc oxide, theabsorption maximum appeared at about 700 millimicrons, and the bandextended to about 900 millimicrons.

The infrared-sensitizing dyes of the present invention can be combinedwith zinc oxide photoconductive material in any of the conventionalmanners to produce photoconductive coatings. No special binders areneeded and any of the high dielectric-insulator binders known forphotoconductive coatings may be used, such as styrene-butadienecopolymers. silicone resins, styrene-alkyd resins, silicone-alkydresins, soya-alkyd resins. polyvinyl chloride, polyvinyl acetate,paraftin and mineral waxes. Nonpolar solvents, such as aromatichydrocarbons, are preferred in preparing the photoconductive layers. Thephotoconductive coatings can be applied to any EXAMPLES 1-3Electrophotographic coatings were prepared and the nearinfrared-sensitizing dyes lR-l and lR-2 were used to sensitize zincoxide. One hundred parts by weight zinc oxide (Photox 80) were mixedwith parts resin (DeSoto 7209, a styrenated-alkyd resin), and reagentgrade toluene was added to adjust the mixture to about 60 percent totalsolids. The mixture was intimately mixed in a Waring Blender for 5minutes. To this mixture was added a solution of either dye lR-l or lR2in methanol. In the case of dye IR-l used in example 1, the amount ofdye added-was 4 X10 g. of dye per 100 g. of zinc oxide, and in the caseof dye 1R-2 used in example 2, the amount of dye added was 6 X 10" g. ofdye per 100 g. of zinc oxide. The mixtures of coatings were then stirredwith a magnetic stirrer for about 2 minutes to allow in each case thedye to adsorb onto the zinc oxide.

The coatings were applied to aluminum foil with a Baker film applicator.The coat weight was maintained at about pounds per ream (500 sheets, by38 inches). After drying, the coated products were conditioned in thedark for 24 hours at SOpercent relative humidity at 74 F.

After conditioning, the products were tested for electrophotographicspeed in a dynamic capacitance electrometer containing a Kodak filterNo. 7-69 and utilizing foot candies of tungsten illumination. By usingthis filter, only light above 710 millimicrons was transmitted withapproximately 75 percent of the light transmitted at 820 millimicrons. Adynamic capacitance electrometer measures the electrophotographicproperties of a zinc oxide coating, for example, charge acceptance, darkdecay, light decay, and residual charge after exposure. Thesemeasurements are recorded on an oscilloscope and photographed to obtaina trace of the electrophotographic properties. FIGS. 1 and 2 representthe traces obtained for the electrophotographic layers of examples l and2 and from the traces it is evident that these coatings werephotosensitive in the near infrared region of the spectrum.

A third product was prepared as above, except that the sensitizing dyeused was an excellent conventional sensitizing dye, bromophenol blue.The dye was used in example 3 in the amount of 4 X10 g. of dye per 100g. of zinc oxide. Under the conditions set out above, thephotoconductive layer did not discharge in the electrometer. This was tobe expected since bromophenol blue absorbs light at 610 millimicrons ina zinc oxide coating, and with the Kodak 7-69 filter, no light wastransmitted to the zinc oxide layer at this wavelength. FIG. 3represents the electrometer curve obtained when bromophenol blue wasused as the sensitizing dye for zinc oxide.

Similar experiments were performed using an SCM Model 33 copier,modified by placing a Kodak 7-69 filter in front of the lens, andbetween the light source and the electrophotographic layer. Theelectrophotographic coatings of examples 1, 2 and 3 were applied topaper at a coat weight of about 20 pounds per ream. The dried productswere exposed in the copier, and those papers coated with the coatings ofexamples 1 and 2 printed to give electrophotographic reproductions of anoriginal. However, the paper having the coating of example 3, whereinthe photoconductive layer was sensitized to visible light withbromophenol blue, failed to print regardless of the dye level used.

We have also found that the intensity of the exposing source can bereduced if zinc oxide is sensitized in the near infrared region. An SCMModel 33 copier was connected so that the exposure lamps were in seriesand operated from a Variac to vary the voltage to the lamps. A constantshutter setting (designated 5) was used, and paper samples bearing thecoatings of examples 1 and 3 were exposed at varying Variac settings. Ata dye level of 6 X10 g. of dye per 100 g. of zinc oxide, thephotoconductive layer containing lR-l produced a print when the voltageto the exposing source was reduced to half the normal amount, whereasthe photoconductive layer containing bromophenol blue, at the same dyeconcentration, would not print. By reducing the voltage to the exposuresource to one-half, the power input was reduced to one-fourth and,consequently, the light output was reduced to about onefourth.

Paper coated with the coatings of examples l-3 were tested forluminosity as measured on a Martin-Sweets Color Brightness Instrument.Luminosity is a measure of the average visible reflectance of the paperover the visible region of the spectrum. At the same electrophotographicspeed, the coatings containing dyes lR-l and lR-2 had at least fivepoints higher luminosity than the coating prepared with bromophenolblue.

EXAMPLE 4 An electrophotographic coating was prepared in similar mannerto that described above in connection with examples l-3. In thisinstance, the near infrared-sensitizing dye ill-3 was used in an amountof about 2 l0 g. of dye per 100 g. of zinc oxide. The coating wasapplied to paper with a Baker film applicator at a coat weight of about20 pounds per ream.

The dried, coated paper was exposed in an SCM Model 33 copier equippedwith a Kodak 7-69 filter in front of the lens. A print of an originalwas produced on the electrophotographic layer, evidencing that the zincoxide has been sensitized in the near infrared region of the spectrum bydye IR-3.

From the above examples, it can be seen that photoconductive zinc oxidecan be sensitized for response in the infrared region of the spectrum.Such photoconductive compositions as described comprise photoconductivezinc oxide, a high dielectric insulator binder for the zinc oxide, andadsorbed to the surface of the zinc oxide a near infrared-sensitizingdye.

As one skilled in the art will readily appreciate, various modificationsmay be made in the examples and descriptions set out above withoutdeparting from the spirit of the invention or the scope of the appendedclaims.

We claim:

1. A photoconductive composition comprising photoconductive zinc oxide,a high dielectric insulator binder for the zinc oxide, and adsorbed tothe surface of the zinc oxide a cyanine dye for sensitizing the zincoxide in the near infrared region of the spectrum, said cyanine dyeselected from those represented by the following general formula:

wherein R and R, each represents a member selected from a sulfoalkylgroup or a carboxyalkyl group; R represents a member consisting of ahydrogen atom; q represents a unit positive integer; X represents anacid anion; and Z and Z, each represents the nonmetallic atoms necessaryto complete a heterocyclic nucleus selected from the group consisting ofa benzothiazole nucleus, or a naphthothiazole nucleus.

2. A photoconductive composition as defined in claim 5 in which the nearinfrared-sensitizing cyanine dye is an anhydronium base of the dyesdefined in claim 1.

3. A photoconductive composition as defined in claim 1 in which the nearinfrared-sensitizing cyanine dye is 2-bis (3 wcarboxyethylbezothiazolyl] heptamethine cyanine iodide.

4. A photoconductive composition as defined in claim 1 in which the nearinfrared sensitizing cyanine dye is [2-bis(3- wsulfopropylbenzothiazolyl)] heptamethine cyanine.

5. A photoconductive composition as defined in claim 1 in which the nearinfrared-sensitizing cyanine dye is [2-bis (3- w-sulfopropylB-naphthothiazolyh] heptamethine cyanine.

6. A photoconductive composition as defined in claim 1 in which the nearinfrared-sensitizing cyanine dye renders the zinc oxide photosensitiveto wavelengths of light above 700 millimicrons.

7 The process of producing a photoconductive composition whichphotosensitive in the near infrared region of the spectrum whichcomprises the step of mixing photoconductive zinc oxide with a highdielectric insulator binder, and add to the mixture a nearinfrared-sensitizing cyanine dye selected from those dyes represented bythe following general formula:

member consisting of a hydrogen atom; q represents a unit positiveinteger; X represents an acid anion; and Z and Z each represents thenonmetallic atoms necessary to complete a heterocyclic nucleus selectedfrom a benzothiazole nucleus, or a naphthothiazole nucleus, whereby thedye is adsorbed onto the surface of the zinc oxide and renders the zincoxide photosensitive to wavelengths of light above 700 millimicrons.

8 The process of claim7 in which the near infrared-sensitizing cyaninedye is an anhydronium base of dyes defined in claim 7.

9. The process of claim7 in which the near infrared-sensitizing cyaninedye is [2-bis (3- w-carboxyethyl benzothiazolyl)] heptamethine cyanineiodide.

10. The process of claim 7 in which the near infrared-sensitizingcyanine dye is [2-bis (3- w-sulfopropyl benzothiazolyl)] heptamethinecyanine.

11. The process of claim 7 in which the near infrared-sensitizingcyanine dye is [2-bis (3- ohsulfopropyl B- naphthothiazolyl)]heptamethine cyanine.

III i l t t PO-WEO UNITED STATES PATENT OFFICE (s/es) CERTIFICATE OFCORRECTION Patent No. 4 D t d November 9, 1971 lnventofls) Giancarlo A,Cavagna et a1 It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

' Column 1, line '7, "absorbed" should read adsorbed 1 Column 2, lines12-17, the minus charge designation over the anion element of thegeneral formula is not clear and should read as follows:

"5-ethoXy- 6 naphthothiazole" should read 5-ethoxy- -naphthothiazoleColumn 3, example 1 of the dye, the title of the structure (IR-l) shouldread: [2-BIS (3- w CARBOXYETHYL] BENZOTHIAZOLYL)] Column 3, line 41, ashould be inserted before blue-black"; line 48, "absorbed" should readadsorbed line 52, "Hthat" should read that example 2 of the dye, thetitle of the structure (Ht-2) should read; [2-BIS (3- {w -SULFOPROPYL]BENZOTHIAZOLYL)] Column 4, line 14, "absorbed" should read adsorbed line18, the should be inserted before "sodium"; example 3 of the dye, thetitle of the structure (IR-3) should read:

-- [2 -BIS (3- {w -SULFOPROPYL],6 -NAPHTHOTHIAZOLYL)] Column 5, line 15,"Blender" should read Blendor line 19, "4 X 10 should read 4 X 10 line20, "6 X 10 should read 6 X 10 line 43, a comma -3- should be insertedafter "2"; line 50, "4 X 10 should read 4 X 10" Column 6, line 4, "6 X10 should read 6 X 10 line 27, "2 X 10 should read 2 X 10 claim I, theminus charge designation over the anion element of the general formulais not clear and should read as follows:

line 63, "nonmetallic" should read non-metallic line 67, "5" should readl lines 71-72, "[2-bis (3 w carboxyethyl bezothiazolyl1" should read[Z-bis 3- f w -carboxyethyl] benzothiazolyl)] lines 74-75, "(Z-bis (3-w-sulfopropyl benzothiazolyl)]" should read [2-bis (3- Z a) sulfopropyl]benzothiazolyl)] UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIONPatent No. 3, 619,154 Dated November 9, 1971 Inventor(s) Giancarlo A,Cavagna et a1 PAGE 2 It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

' Column 7, lines 2-3, "[2--bis (3- a) -sulfopropyl -naphthothiazolyl)]"should read, [2bis (3--{ u) -sulfopropyl] ,3 -naphthothiazolyl)] line 9,is should be inserted before "photosensitive"; line 10, "step" shouldread steps line 11, "add" should read adding claim 7, the minus chargedesignation over the anion element of the general formula is not clearand should read as follows:

Column 8, line 3, "nonmetallio" should read non-metallic line 12, "{2-bis (3- w oarboxyethyl benzothiazolylfl" should read [2-bis 3- 2w-carboxyethyl] benzothiazolyl)] lines 15, 1s "[Z-bis (3-60 -sul;fopropylbenzothiazolyl)]" should read [2-bis (3-50 -sulfopropyl]benzothiazolyl)] lines 18, 19 "[Z-bis (3- w -sulfopropyl fl-naphthothiazolyl)]" should read [2-bis (ii-{w -Sulf0pr0pyl] ,6-naphthothiazolyl)] Signed and sealed this 15th day 01 February 1972.

(SEAL) Attest:

EDWARD M.FLETCHEB JR. ROBERT GOTTSCHALK Attesting Officer" Commissionerof Patents

2. A photoconductive composition as defined in claim 5 in which the nearinfrared-sensitizing cyanine dye is an anhydronium base of the dyesdefined in claim
 1. 3. A photoconductive composition as defined in claim1 in which the near infrared-sensitizing cyanine dye is (2-bis (3 omega-carboxyethyl bezothiazolyl) heptamethine cyanine iodide.
 4. Aphotoconductive composition as defined in claim 1 in which the nearinfrared sensitizing cyanine dye is (2-bis(3- omega -sulfopropylbenzothiazolyl)) heptamethine cyanine.
 5. A photoconductive compositionas defined in claim 1 in which the near infrared-sensitizing cyanine dyeis (2-bis (3- omega -sulfopropyl Beta -naphthothiazolyl)) heptamethinecyanine.
 6. A photoconductive composition as defined in claim 1 in whichthe near infrared-sensitizing cyanine dye renders the zinc oxidephotosensitive to wavelengths of light above 700 millimicrons.
 7. Theprocess of producing a photoconductive composition which photosensitivein the near infrared region of the spectrum which comprises the step ofmixing photoconductive zinc oxide with a high dielectric insulatorbinder, and add to the mixture a near infrared-sensitizing cyanine dyeselected from those dyes reprEsented by the following general formula:8. The process of claim 7 in which the near infrared-sensitizing cyaninedye is an anhydronium base of dyes defined in claim
 7. 9. The process ofclaim 7 in which the near infrared-sensitizing cyanine dye is (2-bis (3-omega -carboxyethyl benzothiazolyl)) heptamethine cyanine iodide. 10.The process of claim 7 in which the near infrared-sensitizing cyaninedye is (2-bis (3- omega -sulfopropyl benzothiazolyl)) heptamethinecyanine.
 11. The process of claim 7 in which the nearinfrared-sensitizing cyanine dye is (2-bis (3- omega -sulfopropyl Beta-naphthothiazolyl)) heptamethine cyanine.